It’s the latest in a series of studies on the effects of various blood pressure drugs on the fatal and incurable brain disease, which is affecting more and more Americans as people live longer.

In this case, it was a type of drug called an ACE inhibitor. Patients at a hospital in Ireland who were taking the drugs anyway to treat their high blood pressure did not worsen at the same rate as patients not taking the drugs, said William Molloy of the Centre for Gerontology and Rehabilitation at University College Cork in Ireland.

“They were not progressing at the same pace as other people,” Molloy told NBC News.

Molloy, who treats Alzheimer’s patients, said he decided to look after he saw other studies suggesting ACE inhibitors might help. He went back through the medical records of 800 patients with Alzheimer’s or vascular dementia. Of them, 360 had test scores the team could use to assess the progress of their disease over six months.

Those taking the ACE inhibitors lost their memory and other thinking abilities at a rate that was about 20 to 30 percent slower than the others, Molloy’s team reported in a study published Thursday in BMJ Open.

“That may not sound like very much,” he said. But over years, the effect would be compounded. And these drugs are available generically and very cheap.

The results would have to be tested in a larger study – preferably a so-called double-blind, prospective study that looked at patients over time, with the drug randomly assigned. That’s important because doctors may have prescribed the drugs to patients for reasons that could also affect the course of their disease, says Dr. Gary Small of the David Geffen School of Medicine at the University of California, Los Angeles and director of the UCLA Longevity Center.

“The doctors decide who goes on the drug and who doesn’t. It might be some other factor that is driving the improvement,” says Small, who was not involved in the study.

Alzheimer’s is a huge and growing problem. Researchers project that the number of Americans living with Alzheimer’s will triple in the next 40 years, which means that 13.8 million will have it by 2050.

Census data project that as the baby boom generation ages, the number of Americans aged 65 to 84 will approximately double by 2050. Currently an estimated 4.7 million Americans have Alzheimer’s, the most common cause of dementia.

Symptoms start with mild memory and thinking problems but as the brain becomes more and more damaged, people lose the ability to find their way around, to care for themselves and, eventually, to eat and drink. “We have nothing that works in dementia at all. We have nothing that prevents it,” Molloy said.

Researchers are desperate to find something that works. Other studies have suggested that blood pressure medication may help – but others show it may actually cause memory loss in some patients.

“The drugs we have for Alzheimer’s dementia are basically symptomatic drugs. They work temporarily. So far as we know there is no specific drug to prevent disease. We know probably that lifestyle choices have an effect.”

People who eat more fruits and vegetables, who exercise, and who stimulate their brains with reading, puzzles and social interaction all can lower their risk of Alzheimer’s. But people who do everything “right” still often get the disease anyway.

Small says this study and the others show that, at the very least, it’s important to take prescribed drugs to control blood pressure.

“One of the weaknesses of this study is that it is an observational study,” Small noted. But he and Molloy both pointed out that this also means it reflects the real world – which is messier than an carefully controlled study in which only certain patients are enrolled.

“Some of the benefit could have been in reducing small stroke risk in the non-Alzheimer patients,” Ashford said via email. “However, it is intriguing that medications may be able to alter the course of dementia, and this is the exciting possibility,” he added.

“This kind of study is very important not just to provide hope, but to lead new research directions that will end up stopping Alzheimer’s disease and other dementing illnesses.”

It’s not clear how blood pressure medications might help prevent Alzheimer’s from damaging the brain. Molloy believes they may work by suppressing inflammation – a process that’s also involved in the damage caused by heart disease.

A study in the journal Neurology showed that, at least in Japanese-American men, taking beta-blockers lowered the risk of Alzheimer’s and general cognitive decline.

That study showed no effect from ACE inhibitors or other blood pressure drugs. But Molloy said ACE inhibitors – which include drugs such as Lotensin, captopril, Vasotec and lisonopril – cross the so-called blood brain barrier and can affect brain tissue.

But studies on various drugs to treat other diseases being tested against Alzheimer’s have disappointed before. Just last May, researchers said they had failed to replicateexperimental findings that a cancer drug could treat Alzheimer’s.

Bceause the drug, Targretin, was already approved as a cancer treatment, doctors know how safe it is and could prescribe it “off label” to treat any condition, including Alzheimer’s. The same could be true of blood pressure drugs, but Small said it’s too soon to start prescribing any blood pressure drugs strictly to help prevent or treat Alzheimer’s.